Begging in the absence of parents: a "quick on the trigger" strategy to minimize costly misses

Nestling begging in the absence of parents may reflect "falsealarms" due to cognitive constraints or signaling activity towardnest mates (sibling negotiation). According to signal detectiontheory, cognitive constraints should result in both false alarms(begging in the absence of parents or to inappropriate stimuli)and misses (failure to beg during parental visits). In our studyof house sparrows, nestling begging in the absence of parentscomprised up to 50% of the begging events at the nest and wasmore frequent at an early age and among hungrier (lower ranked)nestlings. In contrast, the probability of begging during parentalvisits was constantly high (80% or more), suggesting that therate of misses must have been low even at an early age. Theseresults have 2 main implications. First, the observation thatbegging in the absence of parents decreases with nestling agefavors the cognitive constraints hypothesis over functionalexplanations such as the sibling negotiation hypothesis. Second,the low proportion of "misses" among young nestlings suggeststhat nestling respond to their cognitive constraints by usinglow decision criteria (a "quick on the trigger" strategy) thatincreases the frequency of false alarms but minimizes costlymisses.     

Great spotted cuckoos respond earlier to the arrival of feeding foster parents and perform less erroneous begging when hungry than their magpie host nest‐mates

In many bird species, parents usually feed the first nestling that starts to beg before its nest‐mates. The pressure to avoid missed feeds could trigger nestlings to perform in erroneous begging in absence of parents, which has the same costs as begging in the presence of parents but without any reward. So, nestlings should try to minimize both erroneous begging and missed feeds simultaneously. The threshold to start begging is predicted to be lower for hungry nestlings and for nestlings that are unrelated to their nest‐mates, because they suffer lower inclusive fitness costs when depriving nest‐mates of food. In line with this idea, we found that brood parasitic great spotted cuckoo nestlings responded sooner than their magpie nest‐mates when an adult arrived to the nest. Under laboratory conditions, nestlings of both species rarely incurred in erroneous begging when food was abundant, but under conditions of restricted food, magpie nestlings increased erroneous begging while cuckoo nestlings did not. Highly conspicuous begging in cuckoos results in an increased predation risk, which could have resulted in stronger selection pressures on cuckoos to avoid erroneous begging, probably resulting in better developed perceptual abilities, allowing cuckoos to perform better than their host nest‐mates.     

Nestling tree swallows (Tachycineta bicolor) alter begging behaviour in response to odour of familiar adults,but not their nests

Communication using chemical cues is important for many taxa, including birds, but the use of olfaction for intraspecific communication has been investigated only recently in passerines and is understudied in nestlings. To address this knowledge gap, we explored whether nestling tree swallows (Tachycineta bicolor) would recognize and respond to chemical cues of conspecifics, specifically testing begging responses to familiar and unfamiliar nest and adult odours. For the nest odour experiment, nests were treated with either orange essential oil or distilled water to create scented and unscented (control) odour environments, respectively. For the adult odour experiment, adults attending the nestlings were considered “familiar adults” and adults attending a different brood in the population were considered “unfamiliar adults.” We found that begging responses of nestlings did not differ in response to orange oil odour or water, but nestlings begged significantly longer and more intensely in response to odours of a familiar than an unfamiliar adult, regardless of adult sex. This provides evidence that tree swallows use chemical cues to alter their behaviour and opens up many exciting avenues of future research.     

Decrease in Alarm Call Response Among Tufted Capuchins in Competitive Feeding Contexts: Possible Evidence for Counterdeception

Animal signals function to elicit behaviors in receivers that ultimately benefit the signaler, while receivers should respond in a way that maximizes their own fitness. However, the best response may be difficult for receivers to determine when unreliable signaling is common. “Deceptive” alarm calling is common among tufted capuchins (Cebus apella nigritus) in competitive feeding contexts, and responding to these calls is costly. Receivers should thus vary their responses based on whether a call is likely to be reliable. If capuchins are indeed able to assess reliability, I predicted that receivers will be less likely to respond to alarms that are given during competitive feeding contexts than in noncompetitive contexts, and, within feeding contexts, that individuals inside or adjacent to a food patch will be less likely to respond to alarms than those further from the resource. I tested these predictions in a group of wild capuchins by observing the reactions of focal animals to alarm calls in both noncompetitive contexts and experimental feeding contexts. Antipredator escape reactions, but not vigilance reactions, occurred significantly less often in competitive feeding contexts than in noncompetitive contexts and individuals adjacent to food patches were more likely to respond to alarm calls than were those inside or further from food patches. Although not all predictions were fully supported, the findings demonstrate that receivers vary their behavior in a way that minimizes the costs associated with “deceptive” alarms, but further research is needed to determine whether or not this can be attributed to counterdeception.     

Ambient noise and the design of begging signals

The apparent extravagance of begging displays is usually attributed to selection for features, such as loud calls, that make the signal costly and hence reliable. An alternative explanation, however, is that these design features are needed for effective signal transmission and reception. Here, we test the latter hypothesis by examining how the begging calls of tree swallow (Tachycineta bicolor) nestlings and the response to these calls by parents are affected by ambient noise. In a field study, we found that call length, amplitude and frequency range all increased with increasing noise levels at nests. In the laboratory, however, only call amplitude increased in response to the playback of noise to nestlings. In field playbacks to parents, similar levels of noise abolished parental preferences for higher call rates, but the preference was restored when call amplitude was increased to the level that nestlings had used in the laboratory study. Our results show that nestling birds, like other acoustic signallers, consistently increase call amplitude in response to ambient noise and this response appears to enhance discrimination by receivers. Thus, selection for signal efficacy may explain some of the seemingly extravagant features of begging displays.     

Effect of alarm calling by male Red‐winged Blackbirds on nestling begging and female provisioning behavior

ABSTRACT Nestling begging and parental provisioning can attract nest predators and reduce reproductive success, so parents and their offspring might be expected to respond adaptively by minimizing predator‐attracting cues when predators threaten nests. Male Red‐winged Blackbirds (Agelaius phoeniceus) are well known for their antipredator alarm calls that contain information about the approach of potential nest predators. We examined the begging behavior of nestlings and the provisioning behavior of females in response to antipredator alarm calls of males to test the adaptive response hypothesis. Playback experiments provided no evidence that alarm calls function to switch off vocal begging; nestlings were equally likely to beg vocally during playback and control periods. Video recordings showed that male alarm calling had no significant effect on inappropriate vocal begging (in the absence of an adult), but significantly reduced the incidence of spontaneous calling (in the absence of begging). Adult females responded to male antipredator alarm calls by delaying their provisioning visits. In addition, although having no significant effect on use of nest‐arriving calls by females, male alarm calling significantly reduced their use of nest‐leaving calls. We conclude that nestling and female Red‐winged Blackbirds respond to male alarm calls in ways that might reduce the risk of predation, but nestlings beg vocally when females arrive to feed them, regardless of male alarm calling, perhaps to avoid a competitive disadvantage with broodmates.     

False alarms and information transmission in grouping animals

A key benefit of grouping in prey species is access to social information, including information about the presence of predators. Larger groups of prey animals respond both sooner and at greater distances from predators, increasing the likelihood that group members will successfully avoid capture. However, identifying predators in complex environments is a difficult task, and false alarms (alarm behaviours without genuine threat) appear surprisingly frequent across a range of taxa including insects, amphibians, fish, mammals, and birds. In some bird flocks, false alarms have been recorded to substantially outnumber true alarms. False alarms can be costly in terms of both the energetic costs of producing alarm behaviours as well as lost opportunity costs (e.g. abandoning a feeding patch which was in fact safe, losing sleep if an animal is resting/roosting, or losing mating opportunities). Models have shown that false alarms may be a substantial but underappreciated cost of group living, introducing an inherent risk to using social information and a vulnerability to the propagation of false information. This review will focus on false alarms, introducing a two-stage framework to categorise the different factors hypothesised to influence the propensity of animal groups to produce false alarms. A number of factors may affect false alarm rate, and this new framework splits these factors into two core processing stages: (i) individual perception and response; and (ii) group processing of predator information. In the first stage, individuals in the group monitor the environment for predator cues and respond. The factors highlighted in this stage influence the likelihood that an individual will misclassify stimuli and produce a false alarm (e.g. lower light levels can make predator identification more difficult and false alarms more common). In the second stage, alarm information from individuals is processed by the group. The factors highlighted in this stage influence the likelihood of alarm information being copied by group members and propagated through the group (e.g. some animals implement group processing mechanisms that regulate the spread of behavioural responses such as consensus decision making through the quorum response). This review follows the structure of this new framework, focussing on the causes of false alarms, factors that influence false alarm rate, the transmission of alarm information through animal groups, mechanisms to mitigate the spread of false alarms, and the consequences of false alarms.     

Complex feeding behaviour by magpies in nests with great spotted cuckoo nestlings

Parent decisions about food allocation are usually based on simple time‐saving rules that optimize their own fitness; however, they can sometimes vary depending on the prevailing ecological conditions both outside and inside the nest. Parent–offspring interactions also become more complex when parents suffer from brood parasitism, which implies that they care for the parasite's eggs and unrelated young. The great spotted cuckoo Clamator glandarius is a specialist brood parasite that uses the magpie Pica pica as its primary host. Here, by filming food allocation by magpie parents in natural non‐parasitized and experimentally parasitized and non‐parasitized magpie nests, we have found that magpie provisioning behaviour is highly complex including two types of feedings apart from normal ones. First, false feedings, when the parent touched the chick's beak but did not leave any food, occurred more frequently when feeding a cuckoo than when feeding magpie nestlings. Second, two types of what we have called coax feedings: 2a) when magpie parents induce a nestling to beg by waking it up by touching it softly with the beak, and 2b) when parents disregard begging signals (always from brood parasitic great spotted cuckoos) while coaxing one non‐begging nestling (always one of their own) to feed it. We suggest that brood parasitism, involving selfish excessively begging nestlings, could have acted as a selective pressure for both false and coax feedings to evolve, as both imply ignoring nestlings that beg too much. We also discuss that these parental responses could have evolved either by a discrimination without recognition mechanism, or, more probably, by a recognition‐based discrimination mechanism.     

Topography and biological noise determine acoustic detectability on coral reefs

Acoustic telemetry is an increasingly common tool for studying the movement patterns, behavior and site fidelity of marine organisms, but to accurately interpret acoustic data, the variability, periodicity and range of detectability between acoustic tags and receivers must be understood. The relative and interactive effects of topography with biological and environmental noise have not been quantified on coral reefs. We conduct two long-term range tests (1- and 4-month duration) on two different reef types in the central Red Sea to determine the relative effect of distance, depth, topography, time of day, wind, lunar phase, sea surface temperature and thermocline on detection probability. Detectability, as expected, declines with increasing distance between tags and receivers, and we find average detection ranges of 530 and 120 m, using V16 and V13 tags, respectively, but the topography of the reef can significantly modify this relationship, reducing the range by ~70 %, even when tags and receivers are in line-of-sight. Analyses that assume a relationship between distance and detections must therefore be used with care. Nighttime detection range was consistently reduced in both locations, and detections varied by lunar phase in the 4-month test, suggesting a strong influence of biological noise (reducing detection probability up to 30 %), notably more influential than other environmental noises, including wind-driven noise, which is normally considered important in open-water environments. Analysis of detections should be corrected in consideration of the diel patterns we find, and range tests or sentinel tags should be used for more than 1 month to quantify potential changes due to lunar phase. Some studies assume that the most usual factor limiting detection range is weather-related noise; this cannot be extrapolated to coral reefs.     

Learning fine-tunes a specific response of nestlings to the parental alarm calls of their own species

Parent birds often give alarm calls when a predator approaches their nest. However, it is not clear whether these alarms function to warn nestlings, nor is it known whether nestling responses are species-specific. The parental alarms of reed warblers, Acrocephalus scirpaceus ("churr"), dunnocks, Prunella modularis ("tseep"), and robins, Erithacus rubecula ("seee") are very different. Playback experiments revealed that nestlings of all three species ceased begging only in response to conspecific alarm calls. These differences between species in response are not simply a product of differences in raising environment, because when newly hatched dunnocks and robins were cross-fostered to nests of the other two species, they did not develop a response to their foster species' alarms. Instead, they still responded specifically to their own species' alarms. However, their response was less strong than that of nestlings raised normally by their own species. We suggest that, as in song development, a neural template enables nestlings to recognize features of their own species' signals from a background of irrelevant sounds, but learning then fine-tunes the response to reduce recognition errors.     

Similarity in the begging calls of nestling Red‐winged Blackbirds

ABSTRACT Although individually distinct begging calls may permit parents to recognize their offspring, birds nesting in dense breeding colonies where fledglings intermingle might benefit from additional adaptations. For example, if the calls of all nestlings in a brood were similar, parents would need to recognize only one brood call instead of the identity calls of each nestling. We recorded nestling Red‐winged Blackbirds (Agelaius phoeniceus) to determine whether their calls function to identify individuals (identity call hypothesis) or broods (brood call hypothesis). We used spectrogram cross‐correlation and dynamic time warping as well as call duration, peak frequency, and frequency range to estimate the similarity of begging calls of nestling Red‐winged Blackbirds. We recorded individual nestlings on day 5 and on day 9 of the nestling period to determine whether calls of individuals were more similar than calls of different nestlings, and whether calls of broodmates were more similar than calls of nestlings from different broods. We found that calls of 8‐d‐old individuals were more similar than calls of different nestlings, but the calls of broodmates were not more similar than those of nestlings from different broods. These results were consistent with the identity call hypothesis. We then compared begging calls of pairs of nestlings recorded separately and together on day 9. We found that the calls of 8‐d‐old nestlings recorded together were more similar than when they were recorded separately. In addition, using playback of begging calls from normal broods and artificial “broods” constructed from the calls of single nestlings, we found that females returned with food sooner in response to the calls of single nestlings (with enhanced call similarity) than to those of normal broods. Our results suggest that similar begging calls may be beneficial for both nestlings and parents, with broodmates fed at higher rates when their calls are more similar and, after fledging, parents needing to recognize only one brood call instead of the identity calls of each fledgling.     

Development of stress response in nestling pied flycatchers

Birds respond to unpredictable events by secreting corticosterone, which induces various responses to cope with stressful situations. However, the evidence is still elusive whether altricial nestlings perceive and respond to external stressors. We investigated the development of adrenocortical stress response to handling-related stressor in nestlings of a small passerine bird, the pied flycatcher (Ficedula hypoleuca). Nestlings were held in isolation from their parents during the experiment to ensure that they indeed respond to handling, not to parental alarm calls. We found that both 9- and 13-day-old nestlings were able to elicit hormonal stress response. Although baseline as well as stress-induced corticosterone levels rose slightly with age, the magnitude of difference between the control and stress-induced levels remained similar in both age groups. However, comparison with adults showed that the stress response of nestlings prior to fledging was still incomplete and significantly lower than in adults. Overall, our results indicate that altricial nestlings do respond to acute stressors, but on the contrary to previous predictions the development of corticosterone stress response during growth period is not gradual and varies remarkably between different passerine species.     

Noise affects porpoise click detections – the magnitude of the effect depends on logger type and detection filter settings

Automatic click detectors and full-bandwidth sound recorders are widely used in passive acoustic monitoring of small cetaceans. Detection of these signals depends on a variety of factors, including signal to noise ratio. Passive acoustic monitoring is often used to study impact of underwater noise on small cetaceans, but as detection probability is affected by changes in signal to noise ratio, variable noise levels may affect conclusions drawn from these experiments. Therefore, we examine how different detectors and filters perform in varying ocean noise conditions. C-PODs and full-bandwidth recorders (Wildlife Acoustics, SM2M+) were deployed at two stations in an environment with fluctuating ambient noise for 42 days. Noise level and harbour porpoise (Phocoena phocoena) click trains simultaneously recorded on both loggers were compared. Overall, we found that porpoise click detections by the algorithm used to analyse full-band recorder data (Pamguard) paralleled detections by the C-POD. However, Pamguard detected significantly more clicks than the C-POD. A decrease in detections was seen for both loggers with increasing noise in the band 20 –160 kHz, in particular for levels above 100 dB re 1μPa rms. We also found that the Pamguard detection function changed the least over varying noise conditions when compared to the C-POD detectors. This study sheds light on the fact that inference of animal presence/absence or density that are based on echolocation cues (here, Porpoise Positive Minutes) shall account for the acoustic environments where probability of detecting signals may be affected by variability in ambient noise levels.     

Modelling antipredator vigilance and flight response in group foragers when warning signals are ambiguous

The trade-off between feeding and vigilance in flocks of birds has been extensively studied and modelled. An assumption of many models is that if one bird spots the predator, it gives a signal and the rest of the flock takes flight. However, it has been observed that birds do not always respond to signals and in fact many signals turn out to be false alarms. Since taking flight is both costly in time and energy, it may be advantageous for birds not to respond to all alarm calls. A model is developed to show under what circumstances birds should respond to a signal. The model predicts that under most, but not all, circumstances, birds should respond to multiple detections but not to single detections. The model also predicts that if birds respond to all flights, they will have to compensate for the time lost to feeding and the greater energy requirement of spending more time in flight, by being less vigilant, and they have a lower probability of survival than birds which only respond to multiple detections.     

Nest helpers improve parental survival but not offspring production in a high‐elevation passerine,the Ground Tit Pseudopodoces humilis

The way in which breeders respond to helping, in terms of either offspring production or their own survival, may reflect the adaptive aspects of a cooperative breeding system. We explore this issue using a 5‐year study of the Ground Tit Pseudopodoces humilis, a facultative cooperative breeder in which 47% of socially monogamous pairs have between one and four close male relatives as helpers. We found that helped nests did not fledge more or heavier nestlings than unhelped nests, and male young from helped and unhelped nests were equally likely to recruit into the local breeding population. However, helped parents of both sexes had a higher probability of survival to the following year than did unhelped parents. These findings suggest that Ground Tit parents with helpers trade current reproduction for personal survival and future reproduction, a strategy favoured by selection to cope with harsh, unpredictable environments such as the Tibetan Plateau.     

Burying Beetle Larvae Discriminate Between Individual Parents and Between Some Classes of Adults

Offspring begging can be triggered by a variety of acoustic, visual or chemical cues from the parents. In many birds, nestlings use information derived from these cues to discriminate between individual parents or different classes of adults. Although begging occurs in some insects, we know very little about discrimination between adults by insect larvae. Here, we examine whether begging larvae in the burying beetle Nicrophorus vespilloides can discriminate between individual parents or different classes of adults. We found that larvae showed no discrimination between male and female beetles, but that they begged more towards breeding beetles than towards non‐breeding ones. These results were robust regardless of whether larvae had been reared in presence or absence of adult beetles, thus suggesting that larval discrimination is based on an innate template that requires no prior exposure to adult beetles. We also found that larvae begged more towards unfamiliar beetles than towards familiar ones, suggesting that they can learn to discriminate between individual parents based on cues about familiarity. We conclude that insect larvae may benefit from discriminating between different classes of adult beetles, as it allows them to lower the costs associated with begging in response to irrelevant environmental cues (costly in terms of wasted effort) and with not begging in response to the presence of caring parents (costly in terms of lost feeding opportunities).     

Parental allocation of food to nestling tree swallows: the influence of nestling behaviour, sex and paternity

Parents are expected to invest more in young that provide the greatest fitness returns. The cues that parents use to allocate resources between their offspring have received much recent attention. In birds, parents may use begging intensity, position in the nest or nestling size as cues to provision the most competitive young or those most likely to survive. It may also benefit parents to invest in young differentially by sex or relatedness if the fitness returns of sons and daughters differ or broods are sired by multiple males. We examined the allocation of food to tree swallow, Tachycineta bicolor, nestlings in relation to their begging behaviour, size, sex and paternity. Provisioning by parents was not related to nestling size, sex or paternity. The begging behaviour of nestlings did not differ with respect to sex or paternity. Both parents were more likely to feed nestlings that begged first or were closer to the nest entrance, suggesting that parents allocate food resources in response to cues that nestlings control. As a consequence, brood reduction was facilitated by biased provisioning within the brood in addition to the nestling size hierarchies created by hatching asynchrony. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Seeing is believing: information content and behavioural response to visual and chemical cues

Predator avoidance and foraging often pose conflicting demands. Animals can decrease mortality risk searching for predators, but searching decreases foraging time and hence intake. We used this principle to investigate how prey should use information to detect, assess and respond to predation risk from an optimal foraging perspective. A mathematical model showed that solitary bees should increase flower examination time in response to predator cues and that the rate of false alarms should be negatively correlated with the relative value of the flower explored. The predatory ant, Oecophylla smaragdina, and the harmless ant, Polyrhachis dives, differ in the profile of volatiles they emit and in their visual appearance. As predicted, the solitary bee Nomia strigata spent more time examining virgin flowers in presence of predator cues than in their absence. Furthermore, the proportion of flowers rejected decreased from morning to noon, as the relative value of virgin flowers increased. In addition, bees responded differently to visual and chemical cues. While chemical cues induced bees to search around flowers, bees detecting visual cues hovered in front of them. These strategies may allow prey to identify the nature of visual cues and to locate the source of chemical cues.     

Innate development of acoustic signals for host parent–offspring recognition in the brood‐parasitic Screaming Cowbird Molothrus rufoaxillaris

Young birds communicate their need to parents through complex begging displays that include visual and acoustic cues. Nestlings of interspecific brood parasites must ‘tune’ into these communication channels to secure parental care from their hosts. Various studies show that parasitic nestlings can effectively manipulate host parental behaviour through their begging calls, but how these manipulative acoustic signals develop in growing parasites remains poorly understood. We investigated the influence of social experience on begging call development in a host‐specialist brood parasite, the Screaming Cowbird Molothrus rufoaxillaris. Screaming Cowbird nestlings look and sound similar to those of the primary host, the Greyish Baywing Agelaioides badius. This resemblance is likely to be adaptive because Baywings discriminate against fledglings unlike their own and provision nests at higher rates in response to Baywing‐like begging calls than to non‐mimetic begging calls. By means of cross‐fostering and playback experiments, we tested whether the acoustic cues that elicit recognition by Baywings develop innately in Screaming Cowbird nestlings or are acquired through social experience with host parents or nest mates. Our results suggest that begging call structure was partially modulated by experience because Baywing‐reared Screaming Cowbird and host nestlings were acoustically more similar as age increased, whereas acoustic similarity between cross‐fostered and Baywing‐reared Screaming Cowbird nestlings decreased from 4–5 to 8–10 days of age. Cross‐fostered Screaming Cowbirds developed begging calls of lower minimum frequency and broader bandwidth than those of Baywing‐reared Screaming Cowbirds by the age of 8–10 days. Despite the observed differences in begging call structure, however, adult Baywings responded similarly to begging calls of 8‐ to 10‐day‐old cross‐fostered and Baywing‐reared Screaming Cowbirds, suggesting that these were functionally equivalent from the host's perspective. These findings support the idea that, although rearing environment can influence certain begging call parameters, the acoustic cues that serve for offspring recognition by Baywings develop in young Screaming Cowbirds independently of social experience.